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The present invention relates to sucker rod operated subsurface pumps. More particularly, the present invention relates to traveling and standing valve assemblies as used on these pumps. More particularly, the present invention relates to cages used in association with such valve assemblies.
A conventional oil well includes a cased well bore with one or more strings of tubing extending downwardly through the casing into the oil or other petroleum fluid contained in the subsurface mineral formation to be produced. The casing is perforated at the level of the production zone to permit fluid flow from the formation into the casing, and the lower end of the tubing string is generally open to provide entry for the fluid in the tubing.
One type of pump conventionally employed in structures of the type described is wedged into an internal constriction or seating nipple formed internal of the tubing below the fluid level. A metallic enlargement on the external body of the pump prevents it from traveling below the seating nipple and resilient seal rings on the body of the pump housing act to form a leak-proof seal between the seating nipple and pump. The pump is generally driven by a mechanical linkage of metal rods, referred to in the trade as sucker rods which extend from the pump to the well surface. The sucker rod linkage is powered in a reciprocating motion by a conventional mechanical apparatus usually called a pumping unit located at the well surface.
The conventional pump itself generally includes a housing through which a piston is reciprocated by the sucker rod linkage. In its simplest form, the conventional pump of the type described often includes a number of ball and seat valves with one such valve associated with the piston or plunger (traveling valve) and another (standing valve) at the inlet port of the housing or barrel of the pump. On the upstroke of the plunger, the ball in the inlet port valve or standing valve is drawn away from its seat and the ball of the outlet port valve or traveling valve is forced over its seat to draw fluid from below the seating nipple and into the housing. On the piston downstroke, the ball in the standing valve is forced onto its seat and the ball in the traveling valve moves away from its seat to allow the plunger to move downwardly through the fluid contained in the housing. On the subsequent upstroke, the closing of the traveling valve forces the fluid above the plunger out of the housing through the outlet ports and into the tubing above the seating nipple and simultaneously fills the housing below the plunger with fluid. Repetition of this cycle eventually fills the tubing string and causes the fluid to flow to the surface.
Ball valve pumps are also relatively limited in theoretical efficiency and cycling rate due to their inherent principle of operation. Any increase in the amount of fluid which can be produced by such a pump usually involves an increase in the driving power and pump dimensions and includes a corresponding decrease in efficiency. Moreover, the valve closure time required for the ball and seat type valves restricts the speed of the pumping cycle and thereby further limits the maximum product on rate of pumps employing these valves.
In operation of a sucker rod pump, the plunger in the barrel is lifting the entire column of oil above the plunger on the upstroke. Thus, the load on the plunger is equal to the weight of the column of oil having a cross-sectional area of the pump plunger. The cross-sectional area of the pump plunger times the length of stroke equals the volume of oil being lifted on each pumping cycle.
A stationary barrel pump has the traveling valve assembly connected to the plunger and the standing valve made up in the lower end of the barrel. A traveling barrel pump has the traveling valve assembled with the barrel and the standing valve on the plunger. Although the present invention is particularly directed to the use of traveling valves, it can also be used as a standing valve assembly. The traveling valve assembly must be designed to allow the fluid that has entered the pump of the previous upstroke to pass through it with the smallest amount of pressure differential during the downstroke cycle of the pump. As the differential pressure increases, weight from the sucker rods directly above the pump is required to force the liquid through the plunger. If enough weight is taken from the rods to allow them to buckle slightly and to come into contact with the inside of the tubing string, then wear occurs both on the tubing string and on the sucker rods. The weight or force required to force the fluid through the traveling valve assembly is dependent upon the viscosity of fluid, the flow capacity of the traveling valve assembly and the pumping rate. As such, it is desirable to lower the force required to move the plunger through the fluid so as to increase pumping rate and overall system efficiency.
Another issue facing the traveling valve assembly is the issue of durability. During the pumping cycle, gas or vapor may occupy the space in the pump above the standing valve and below the traveling valve. On the downstroke of the pump, pressure is built up between the two valves until that pressure becomes slightly greater than the force of the fluid on top of the traveling valve due to the weight of the fluid above it. Water weighs 0.43 pounds per foot such that if the oil column weighs 0.4 pounds per foot, then in a well with the pump landed 5,000 feet from the surface, the pressure on the top of the traveling ball is 2,000 pounds per square inch. In normal pumping operations, with little or no gas in the pump at the start of the downstroke, this pressure is built up very quickly and the ball moves off of the seat and up against the top side of the cage while the plunger is at low velocities. If the pump is filled equally with liquid and gas, the traveling ball will remain on the seat until the plunger reaches midpoint on the downstroke where it will come into contact with the liquid in the pump. This will be at maximum plunger velocity. Pressure builds up immediately and forces the ball off of the seat with extreme force impacting the top inside of the cage. This force can cause damage or even break the cage in severe cases. As such, it is necessary to design the cage in such a manner so as to minimize the effects that this pumping operation can cause.
It is an object of the present invention to provide a valve assembly which maximizes the flow capacity of the fluid of the cage.
It is another object of the present invention to provide a valve assembly which minimizes the effects of traveling ball movement within the cage.
It is another object of the present invention to provide a valve assembly which maximizes the suspension time of solids within the fluids.
It is a further object of the present invention to provide a valve assembly which enhances flow capability of the fluid through the cage and through the tubing string.
It is a further object of the present invention to provide a valve assembly for an oil pumping system which maximizes efficiency or operational capacity of the oil pump.
It is a further object to provide a valve assembly which will withstand th severe forces associated with fluid pound conditions.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.
The present invention is a valve assembly for an oil pumping system comprising a shell, a seat affixed at a lower end of the shell, a ball moveably positioned in the shell and a cage positioned within the interior passageway of the shell. The ball has a diameter greater than the interior diameter of the seat. The cage has an open bottom facing the seat and an open top facing the upper end of the shell. The cage has an upper portion, a lower portion and a ball retaining section. The cage has a first ported area formed in the lower portion between the bottom and the ball retaining section. The cage has a second ported area formed in the upper portion between the ball retaining section and the top.
In the present invention, the shell has an annular shoulder extending into the interior passageway. The seat has an end abutting the shoulder. A seat retainer has an upper end abutting a bottom of the seat such that the seat is fixedly interposed between the upper end of the seat retainer and the shoulder of the shell. The shell has interior threads at the lower end. The seat retainer has external threads at an upper end thereof threadedly affixed to these interior threads. The seat retainer has an interior passageway therethrough.
In the present invention, an elastomeric ring is positioned generally against the top of the cage. The elastomeric ring is retained within the interior passageway of the shell. A bushing has a lower end affixed within the upper end of the shell and abutting the elastomeric ring on a side opposite the cage.
The ball retaining section of the cage extends across an interior of the cage. The ball retaining section is concave with a contour generally matching a contour of the ball. The ball retaining section has a hole formed therethrough so as to open at one end to the first ported area and the opposite end to the second ported area.
The cage has a first flanged surface at the top thereof and a second flanged surface at the bottom thereof. Each of the first and second flanged surfaces has a diameter greater than a remainder of the cage. The diameter of each of the first and second flanged surfaces generally matches the diameter of the interior passageway of the shell. The first ported area has a plurality of ports opening through a wall of the cage. The second ported area has a plurality of ports also opening through a wall of the cage. The plurality of ports of the second ported area are helixed.